Sex- Linked · PDF fileExamples: Cri du Chat syndrome, Angelman’s syndrome,...

Sex- Linked Traits,

and Human Genetics

NOTES ch14

Karyotype- Map of all of the chromosomes

in a cell

Karyotype

Has 46 Chromosomes (23 pairs, Last pair is the sex

chromosomes XY : Male, XX: Female)

Enables scientists / doctor’s to view the chromosomes of

a person, plant or animal

Detection of abnormalities/ gender

Chromosomal defects

What is a mutation?

__________________________________________

There are two types of mutations that can occur

in gamete cells:

1. Gene mutation: affect only one gene.

Examples: point and frameshift.

2. Chromosomal mutation: affect the number or

structure of chromosomes. Usually involves many,

many genes.

5 types of Chromosomal Mutations

1. Deletion

2. Duplication

3. Inversion

4. Translocation

5. Non-disjunction

1.Deletion: Involves the loss of all or part

of a chromosome

Examples: Cri du Chat syndrome, Angelman’s

syndrome, Prader-Willi syndrome, Miller-Dieker

syndrome

2.Duplication-Involves the production of

extra copies of parts of the chromosome

Examples: Fragile X syndrome, Beckwith-Wiedeman

syndrome

3.Inversion: Reverses the direction of parts of a

chromosome

4.Translocation: When one part of a chromosome

breaks off and attaches to another chromosome.

Example: Edward’s syndrome

5. Non-disjunction:

Means “not coming apart”.

When homologous chromosomes fail to separate

properly during meiosis.

Results in abnormal numbers of chromosomes.

Normal is two of each type of chromosome.

Trisomy means a person has an extra copy of a

chromosome.

Review Question

Which parent determines the sex of an offspring?

________________

How?

_______________________________________________

Sex linked traits… what are they?

those traits that are controlled by genes

on the X or Y chromosomes.

The Y chromosome is much smaller than

the X chromosome and only contains

fewer genes. Most sex-linked traits are on

the X chromosome.

Question:

Why is a male more

likely to inherit a sex-

linked genetic

disorder?

A male can inherit a recessive trait if the gene for the

trait is present on his X chromosome, because Y

chromosome cannot hide the trait.

A female must have the recessive trait on both X

chromosomes for that trait to show

Previous Knowledge :

What are some sex-linked genetic disorders that you

already know?

__________________________________________

__________________________________________

________________________________________.

Duchenne Muscular Dystrophy

SCID- severe combined immune deficiency disorder

Colorblindess

Hemophilia

* Klinefelter’s Syndrome and *Turner’s syndrome caused

by chromosome abnormalities of the sex chromosomes

but, the genes are not located on the X chromosome.

Punnett Squares with Sex-Linked Traits

In humans, hemophilia is a sex-linked trait. Having hemophilia

is recessive (Xh) to being normal (XH). The heterozygous

female is called a carrier. Cross a carrier female with a

normal male.

__ XHXh __ X __ XHY ___

What are the phenotypic ratios?

X H Xh

X

H

Y

TRACKING TRAITS AND GENETIC

DISORDERS

How do we trace traits

or genetic diseases

through families?

Pedigrees! What is a pedigree?

A chart that shows relationships within a family that is

used to show inheritance of traits.

INTERPRETING AND DRAWING PEDIGREES

1. squares represent males, circles represent females

2. shaded shapes represent those family members having

the trait being traced (or disease)

3. un-shaded shapes represent family members not

affected by trait or disease.

4.½ shaded square or circle indicates a carrier

(heterozygous) individual.

5.Horizontal line connecting circle to square indicates a

marriage and/ or a generation.

6.Vertical line with a bracket connecting circles or

squares to a marriage line indicates siblings (oldest child

first)

7. Roman numerals or capital letters indicate

generations.

Symbols used : do not write

Royal disease

Human Traits

Traits can be autosomal (on a chromosome other than

the sex chromosomes) or on the sex chromosomes.

Almost all of human traits are polygenic.

Human traits are also influenced by the environment.

Recessive Autosomal Disorders

Inherited by recessive alleles.

1. PKU- cannot process an amino acid

2. Albinism

3. Tay Sachs- lipid build up in brain caused by a single

nitrogen base change (A, C, T,G)

4. Cystic Fibrosis – excessive mucous in lungs

Dominant Autosomal Disorders

Caused by Dominant alleles

Examples: 1. Achondroplasia – dwarfism

2. Huntington’s – mental deterioration

3. Hypercholesterolemia- heart disease due to

excessive cholesterol

4. Marfan’s syndrome- lanky, cardiovascular issues

Codominant disorders

Sickle cell disease/ anemia

Blood cells are abnormal or sickle-shaped

In a heterozygous individual, both normal and sickle-

shaped are present.